Process for the production of carbon fibers

ABSTRACT

In the production of carbon fibers wherein a carbon-containing fiber-forming material is spun as a solution, the spun-filaments are converted to solid fibrous material, and the fibrous material is carbonized, the improvement which comprises including in said solution at least one fiber-forming high polymer at a concentration of about 0.001 to 10 percent by weight and a greater amount of a carbon source comprising at least one carboncontaining organic material having a softening or melting point in excess of about 80* C., whereby the solution of said carbon containing material is rendered spinnable by addition of said fiber-forming high polymer, said carbon containing organic material serving as the source of carbon for the carbon fiber; the fiber may thereafter be graphitized. The spinning solution used for fiber production is preferably a solution in a volatile solvent so that it may be dry spun. The carbon source in said solvent by itself would not be spinnable and may be a monomer or low polymer.

United States Patent Mansmann et al.

PROCESS FOR THE PRODUCTION OF CARBON FIBERS Inventors: Manfred Mansmann;Gerhard Winter, Krefeld; Gottfried Pampus; Hildegard Schnoring, both ofLeverkusen; Nikolaus Schon, Wuppertal- Elbergeld, all of GermanyAssignee: Bayer Aktiengesellschaft, Leverkusen, Germany Filed: Oct. 7,1970 Appl. No.: 78,943

Foreign Application Priority Data 0a. 17, 19:69 Ger many ..P 19 52 388.7

US. Cl. ..423/447, 264/29, 264/ 176 F Int. Cl. ..C0lb 31/07 Field ofSearch ..'....23/209.1, 209.2, 209.4; 264/29, 204, 205, 207, 176; 260/6,8, 9 R,

17, 17.4 R, 17.4 ST, 17.4 SG

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS3,820,609 10/1963 Japan ..23/209.l

Primary Examiner-Edward J. Meros Attomey-Burgess, Dinklage & SprungABSTRACT In the production of carbon fibers wherein a carboncontainingfiber-forming material is spun as a solution, the spun-filaments areconverted to solid fibrous material, and the fibrous material iscarbonized, the improvement which comprises including in said solutionat least one fiber-forming high polymer at a con centration of about0.001 to 10 percent by weight and a greater amount of a carbon sourcecomprising at least one carbon-containing organic material having asoftening or melting point in excess of about 80 C., whereby thesolution of said carbon containing material is rendered spinnable byaddition of said fiber-forming high polymer, said carbon containingorganic material serving as the source of carbon for the carbon fiber;the fiber may thereafter be graphitized. The spinning solution used forfiber production is preferably a solution in a volatile solvent so thatit may be dry spun. The carbon source in said solvent by itself wouldnot be spinnable and may be a monomer or low polymer.

16 Claims, No Drawings Carpenter et al ..23/209.l 1 I PROCESS FOR THEPRODUCTION OF CARBON FIBERS This invention relates to the production ofcarbon fibers predominantly from materials which are not normallyspinnable as a solution.

Numerous proposals are found in the literature for' the production ofcarbon fibers. Carbon fibers are generally produced through carbonizingan organic starting material in the form of fibers by a thermaltreatment in an inert gas. The carbon fibers thus produced are convertedinto graphite fibers by further heating to temperatures of up to about 3,000 C.

To produce strong and flexible carbon fibers, the starting fibers mustnot only be readily producible but also fulfil the following importantrequirements:

a. The material must not pass through a tacky or liquid state in thecourse of carbonization which would cause the fibers to stick togetherand lose their flexibility.

b. The carbon residue should be as high as possible. c. In order toobtain high volume/time yields in the production process, the originalfiber must be able to withstand a rapid temperature increase withoutloss in strength and flexibility of the resulting carbon fibers. Thestarting material must be readily available in a fibrous form. Thestarting material should be inexpensive.

Numerous starting materials have been proposed but none of them fulfilall these conditions. Carbon and graphite fibers have been obtained, forexample, by the carbonization and, where indicated, the graphitizationof natural or regenerated cellulose, polyacrylonitrile, polyvinylalcohol, polyvinyl chloride and specially pretreated woolen fibers (0.Vohler, E. Sperk: Ber. Dtsch. Keram. Ges. 43 [1966] pages 199208).

According to French Patent Specification No. 1,465,030, molten bitumenor tar pitch is spun into fibers at temperatures of at least 240 C., andthese fibers are then used as starting fibers for the production ofcarbon and graphite fibers. The object of this process is this processis to enable inexpensive fiber materials to be used as startingmaterials for carbon fibers, which are not normally available in fibrousform. Apart from the fact that the material has tobe spun at a hightemperature, one of the major disadvantages of the process is that thestarting material must first be adjusted to a quite specific C/H ratioin a separate process step, and the tar fibers must be renderedinfusible before the carbonization by pretreating them with ozone orperoxides, followed by oxidation in air.

Of all the many carbon compounds, therefore, only a very few substancescan be used as starting materials for carbon fibers. One of the reasonswhy some of the substances which appeared to be suitable could not beused was that they are not available in a fibrous form. If a substanceis to be spun from the fluid phase into fibers by the conventionalmethods of the man-made fiber industry, it is essential for the spinningprocess that the fluid phase should be spinnable. The spinna bility of afluid substance is manifested by the fact that when a glass rod isdipped into such a solution and removed from it, the liquid is drawn upwith the rod as a thread of substantial length and does not, as isnormally the case, drip from the rod. Spinnability is a quite specificstate. The number of spinnable substances is accordingly limited andsubstantially comprises the known materials ofthe man-made fiberindustry.

In this context, the term carbonization is understood to mean the heattreatment of an organic substance to temperatures below 2,000" C.,preferably to about 1,000 C., heating being carried out at a temperatureof at least about 400 C. in an inert gas at normal or reduced pressure.Graphitization is understood to mean a heat treatment at temperatures ofbetween 2,000 C. and about 3,000 C. under a protective gas atmosphere.

It is accordingly an object of the invention to solve the problem byproviding a simple method of producing spinnable solutions of numeroussubstances which are not spinnable as such but which otherwise fulfilthe conditions for the production of carbon fibers.

The process according to the invention for the production of carbon andgraphite fibers by carbonization, and if indicated graphitization, ofstarting fibers which contain carbon is characterized in that thestarting fibers which contain carbon are produced by spinning solutions,which, in addition to at least one organic substance which has a meltingor softening point above approximately C. and which can be decomposed tocarbon by a carbonization treatment, also contain 0.001 to 10 percent byweight of at least one fiber-forming high polymer substance which has achain structure and which is soluble in the solvent.

In accordance with this invention, determination of the spinnability iscarried out by a process which has been described in the literature andwhich is similar to the usual process employed in the case of dryspinning. The liquid under investigation is extruded from a nozzle underpressure and the length in centimeters of the uninterrupted filament ofliquid, measured up to the point where it breaks up into individualdroplets, is taken as a measure of the spinnability (Kolloid-Zeitschrift 61 [1932] page 258). In the measurements carried out, thesolutions were extruded at room temperature under a pressure of 0.5atmosphere gauge from a nozzle which had a nozzle diameter of 400microns and a length of nozzle duct of 17 mm.

It was surprisingly found that a solution of an organic substance whichis suitable as a starting material for the production of carbon fibers,i.e. which can be decomposed into carbon by a carbonization treatmentbut which is not spinnable as such (hereinafter termed the carbon sourceor source of carbon) can be rendered spinnable in a simple manner by thepresence of small quantities of high molecular weight linear polymers(hereinafter referred to as fiber-forming substances) or fiber-forminghigh polymers. The fiber-forming substances are added in quantities ofabout 0.001 to 10 percent by weight, preferably about 0.01 to 5 percentby weight. For allpractical purposes, these concentrations aresufficient for achieving spinnability. Furthermore, it is one of thecharacteristics of the'invention that spinning can be carried out withinexpensive carbon sources, which are by-products or waste productsofother processes, with addition of high polymer fiberforming substancesin only very small'amountwith obviouseconomic advantage.

The concentration of the carbon source in the'solution can vary withinwide limits. Solutions having concentrations of from about 5 to 60percent can be used but the concentration of the carbon source in thesolutions used for spinning is generally between about and 40 percent byweight.

The process enables carbon and graphite fibers to be obtained for thefirst time from numerous organic starting materials which could nothitherto be used since they could not be obtained in the form of fibers.Thus it is now possible to process inexpensive by-products or wasteproducts of natural or synthetic origin into fibers from which carbonand graphite fibers can then be obtained. The necessary condition forthe suitability of an organic material is a sufficiently high carbonresidue in the carbonization process which of course depends upon theinitial carbon content and should preferably be at least about 10percent by weight of the starting material. In addition, the materialmust not pass through a liquid or tacky state in the course ofcarbonization. This is ensured whenever the melting point issubstantially above the decomposition temperature.

The following are mentioned as examples of the large number of suitablestarting materials which are available in practice: Carbohydratederivatives such as starch, partly degraded or oxidized starch, dextrin,hemicellulose, cellulose derivatives such as methyl cellulose, vegetablegums, polymeric sugar derivatives such as polyuronic acids, e.g. pectin,pectinic acid or alginic acid, proteins such as casein, gelatine or fishglue, organic acid derivatives which are capable of internal saltformation such as glycocol or betaine, sulfonic acids, theirsubstitution products and their salts, especially ammonium slats,lignin, ligninsulfonic acid and its salts, in particular ammonium ligninsulfonate.

According to the process. of the invention, substances whose melting orsoftening point is below the decomposition temperature may also be usedas carbon sources provided the fibers spun from them are treated so thatthey will maintain their fibrous character during the actualcarbonization, e.g. as by being rendered in-. fusible. In this case, themelting or softening point of the substances used as carbon sourcesshould not be substantially below about 80 C. Numerous measures arealready known in the literature by which fiber materials which softenbefore their decomposition can be rendered infusible.

A process for producing carbon or graphite fibrous material from astarting material which contains wool has been claimed in GermanAuslegeschrift 1,255,629. Since the starting material which containswool would lose its fibrous structure by a heat treatment, this must beprevented by special measures which comprise heating the startingmaterial to about 200 C. with access of air at such a rate that thetemperature rises by from 5 to 50 C. per hour. Heating is then continuedto a temperature of about 300 C. under a restricted air supply and at arate of temperature increase of 1 to 10 C. per hour, and the temperatureis then raised to about l,000 C. with exclusion of air at a rate oftemperature increase of 10 to 100 C. per hour, and'heating is carriedout at least partly in an atmosphere which contains formaldehyde,ammonia and/or carbon dioxide.

According to French Patent Specification No. 1,465,030 which has alreadybeen cited, tar fibers can be rendered infusible by a treatment withozone or peroxides followed by oxidation in air. In Belgian PatentSpecification No. 718,561, fibers of vinyl chloride copolymers,polyvinyl alcohol derivatives and/or polyvinyl alcohol are renderedinfusible by a treatment with acid condensing agents below the softeningtemperature of the fibers. The condensing agents used are preferablyconcentrated sulfuric acid or difluoroand hexa-fluorophosphoric acid.Polyvinyl alcohol, which melts at about 230 C. in inert gas, can berendered infusible simply by a preliminary oxidation with air. A. Shindoet al. (Polymer Preprints, 9, No. 2 [1968] page 1,327) moreover foundthat preoxidized polyvinyl alcohol yields a much higher carbon residuewhen pyrolysis is carried out in the presence of gaseous HCl than whenit is carried out under inert gas.

The following are mentioned as examples ofthe large number of startingmaterials which soften or melt when heated and therefore have to berendered infusible prior to carbonization: Polyvinyl alcohol, polyvinylacylates, polyvinyl chloride, polyolefins, polyesters, polyethers,polyanhydrides, polyurethanes, polyamides, polyureas, phenolformaldehyde resins, both as pure polymers and in the form of theircopolymers, graft polymers and derivatives and the like. In contrast tothe fiber-forming substances, these polymers which are used as carbonsources need not have a linear polymeric structure and they also differfrom fiberforming substances by having a lower degree of polymerization.Addition of a fiber-forming substance also confers spinnability onsolutions of these polymers.

Carbon sources in accordance with this invention are therefore any lowmolecular weight or higher molecular weight organic substances whichhave melting or softening points above approximately C., are soluble ina solvent and can be decomposed to carbon by a carbonization treatment.Carbon sources include especially those substances which in addition tohaving the above mentioned features have a spinnability of less than 10cm as 10 percent solutions. The carbon residue from carbonization shouldbe at least about 10 percent by weight of the carbon source.

It must be emphasized that the process according to the invention makesit possible for the first time to convert molecular disperse solutionsand those of low polymers, in particular those which have a degree ofpolymerization below about 50, into fibers by a dry spinning process (asdefined in Ullmanns'Encyklopadie der technischen Chemie 7 [1956] page263) and hence make them available as starting materials for carbonfibers. Compounds of this type frequently have the advantage overmacromolecular substances of being more soluble so that they can be usedin higher concentrations in solutions.

The fiber-forming substances which are used according to the inventionare characterized not only by their linear polymer structure but alsoby'their degree of polymerization or molecular weight. It is only abovea certain degree of polymerization that solutions of high polymersmanifest the property of spinnability at concentrations below 5 percent.The choice of the fiberforming substance depends on the particularsolvent used. For aqueous solutions, water-soluble high polymers areused, preferably polyethylene oxide, polyacrylamide or acrylicacid/acrylamide copolymers and the like. In organic media, one may usenot only the substances mentioned above but also other high polymersubstances such as polystyrene, polyisobutylene, polymethylmethacrylate,polyisoprene, and the like.

Solutions of linear polymeric substances have been in use for a longtime in spinning processes of the manmade fiber industry. Thesesolutions also have the property of spinnability but the molecularweights and degrees of polymerization of the substances used for thesepurposes are substantially lower than in the substances used accordingto the invention. These solutions are not sufficiently spinnable untilthey have concentrations in the region of 25 to 45 percent. Thus, forexample for the production of polyacrylonitrile fibers a 25 percentsolution of a polyacrylonitrile having a molecular weight of 35,000 to50,000, which cor responds to a degree of polymerization of 660 to 950,is spun in dimethyl formamide (Ullmanns Encyklopadie der technischenChemie, 7 [1956]). If such substances are made up into 0.01 to 5 percentsolutions in a suitable solvent, they are not spinnable. When extrudedthrough a nozzle, they only form a series of droplets but no coherentfibers.

The spinnability of high polymer solutions at the low concentrationsused in the process of the present invention depends decisively on thedegree of polymerization of the substance used. To illustrate this fact,the conditions in aqueous and organic media will now be explained withthe aid of a few examples.

2 percent aqueous solutions of polyethylene oxide may achieve variousvalues of spinnability depending on the molecular weight or degree ofpolymerization. The solution of a polyethylene oxide A having a degreeof polymerization DP of 5,450 has a spinnability of only 30 cm, thesolution of a polyethylene oxide B (DP 17,000) has a spinnability of 130cm, polyethylene oxide C (DP 68,200) a spinnability of 225 cm, and thespinnability of a polyethylene oxide D with DP 136,400 is already farabove 300 cm. To specify the substances more accurately, the limitingviscosity number [1;] determined in water at 35 C. at a shear stressof1-= 12.5 dyn/cm is also indicated (Table 1).

The limiting viscosity number also known as the intrinsic viscosity isdefined as follows:

1;,= relat. viscosity 1 /1 071 viscosity of the solution; 1 viscosity ofthe solvent; c concentration in g/l 00 ml.

At a degree of polymerization of 136,400 [1;] 9.15), a 1.5 percentaquous polyethylene oxide solution already has a spinnability of 300 cm.If a solution of a carbon source which is not spinnable as such contains1.5 percent of this polyethylene oxide, this solution will have aspinnability of several meters. The spinnability of the high molecularweight polyethylene oxide has been transmitted to the particularsolution. If

similarly high values of spinnability are to be achieved with apolyethylene oxide of low degree of polymerization, the concentration ofthis polyethylene oxide must be correspondingly higher. Thus, forexample a spinnability of 300 cm will also be achieved with apolyethylene oxide having a degree of polymerization.

of 6,800 if the aqueous solution contains 2.5 percent.

For aqueous systems, polyacrylamides or acrylamide/acrylic acidcopolymers and salts thereof are also suitable. Thus, for example, acopolymer of acrylamide and acrylic acid which consists to an extent ofpercent of polyacrylamide and which has a degree of polymerization of14,080 has a spinnability of 300 cm when present as a 1.7 percentaqueous solution. A higher molecular weight product with a degree ofpolymerization of 70,400 has a spinnability of 300 cm when itsconcentration in water is only 0.25 percent. The inherent viscosity (In1 r)/c (determined in water, 25 C., pH 7; 0,05 percent solution with 0.1percent NaCl at 'r 0.98 dyn/cm where c is the concentration in gram perml. of the solvent) of this product is 35. The proportion of acrylamideto acrylic acid in' the copolymers may have any value between 0 l and 10. A copolymer containing 2.5 percent of acrylamide (97.5 percent ofacrylic acid) has a spinnability of 210 cm when present as a 0.8 percentsolution. Similarly high spinnability is also achieved if the acrylicacid of TABLE 2 Substance Degree of Concentration Spinnabilitypolymerization Percent by (cm) wt. in CH,C1,

Polystyrene A 1,038 3 l Polystyrene 8 20,200 3 10 Polystyrene C 25,000 320 Polystyrene D 27,900 3 50 Polystyrene E 34,600 3 1 l0 Polystyrene F125,000 0,15 300 Similar conditions are also found in the case of otherhigh polymers, e.g. solutions of polyisobutylene in trichloroethylene(Table 3).

TABLE 3 Substance Degree of Concentration Spinnability polymerization(Percent by (cm) weight in trichloroethylene) Polyisobutylene A 6,900 34 B 23,600 3 20 C 49,000 3 60 D 85,500 1.5 300 The 3 percent solution inCH Cl of a polymethyl methacrylate with a degree of polymerization of3,600 is found to have a spinnability of cm whereas at a degree ofpolymerization of 15,000 a 2 percent solution in CH Cl has aspinnability of 300 cm. 3 percent solutions of polyisoprene, e.g. intoluene or trichloroethylene, are also spinnable (degree ofpolymerization DP 25,000).

Polyethylene oxide which can be spun in the form of an aqueous solutionalso manifests this property in organic solvents such as CH Cl Anincrease in spinnability with the degree of polymerization is againobserved here. The effect is even greater in CH Cl than in water.Polyethylene oxide with a degree of polymerization of 6,800 has aspinnability of 300 cm already at a concentration of only 0.2 percent.

These phenomena can also be produced with other high polymers which havea chain structure, including e.g. vinyl polymers an copolymers, diolefinpolymers, polydienes, substituted polyethers and thioethers,

polyesters, polyamides, polypeptides, polysaccharides,

polysiloxanes, and mixtures of these substances, and the like. Thelimits for the occurrence of spinnability may shift slightly accordingto the nature of the high polymer substance and of the solvent used. Inall cases, however, one observes that substances of high limitingviscosities numbers [1 or high degrees of polymerization are spinnablein solutions of very low concentration, and this spinnability can betransferred to solutions of carbon sources. When using polymersubstances which have a low degree of polymerization as found in mostcommercially available products, however, it is found that dilutesolutions are not spinnable, just as polyethylene oxide could not bespun at degrees of polymerization of below 2,000.

Fiber-forming substances within the meaning of the present invention aretherefore high polymer organic soluble compounds which have a linearpolymeric structure. They preferably have degrees of polymerizationabove approximately 2,000.

The usual commercial solvents may be used. Their choice will depend onthe solubility of the carbon source. It is advantageous to use solventswith boiling points below about 200 C. The solvent used is preferablywater.

To produce the spinning solutions, a solution of the fiber-formingsubstance is added to the solutions of the carbon source until thesolution iscapable of producing fibers, i.e. until sufficientspinnability is obtained, which generally occurs in the region of from0.01 to 2 percent by weight of the fiber-forming substance based on thetotal amount of the solution. If desired, the carbon source may also bedissolved directly inthe solution of the fiber-forming substance. Theconcentration of the carbon source may vary within wide limits. At highconcentrations, a lower concentration of the fiberforming substance isgenerally sufficient whereas at lower concentrations of the carbonsource it is necessary to use larger quantities of the fiber-formingsubstance. The quantity also depends on the nature of the solution, morehighly viscous solutions generally requiring less fiber-formingsubstance than thin, very liquid solutions. The spinnability of thesolution should be at least above 50, advantageously at least above 100and preferably at least above 200.

In some cases, it has been found advantageous to adjust the spinningsolution to a certain pH value, either because the solubility of thecarbon source is thereby increased or because the viscosity. of thespinning solution depends upon the pH. In some cases, solidification ofthe fiber in the spinning column can be accelerated by a change in pH.Thus, for example an ammoniacal solution of ammonium lignin sulfonatewhich contains polyethylene oxide is highly fluid whereas the samesolution at or near a neutral pH is much more viscous. When spinning theammoniacal solution, the pH in the fiber falls due to the evaporation ofNH and the viscosity therefore rises. This, together with the increasein concentration due to evaporation of solvent, leads to solidificationof the fiber. To adjust to a pH below 7, the known inorganic acids,especially hydrohalic acids,-may be added. it is preferable, however, touse organic monoor polycarboxylic acids such as formic acid, acetic acidor oxalic acid, advantageously in quantities of from about 1 to 60percent.

The spinning solutions thus obtained have numerous advantageousproperties. Apart from having good spin-v nability, the relatively lowviscosity and the ease with which they can therefore be handled areadded advantages. The viscosity of these solutions may lie between about0.1 to 100 poise but preferably from about 1 to 10 poise, thereforebelow the values usually required for spinning processes. The spinningsolutions are therefore easily to be filtered, easily to be degasified,and'can easily be pumped through pipes.

Spinning may be carried out by either the wet or the dry spinningprocess but a conventional dry spinning process is preferably employed.The solutions are spun from a multiaperture spinning die substantiallyat temperatures below the boiling point of the solvent used. Thefilaments pass through a spinning column which can be heated to severalhundred degrees centigrade, depending on the solvent used, and which maybe traversed by a current of air or inert gas in the usual manner. Inthe column, the fibers are drawn out to a diameter of from about 50 toabout 1 micron. At the same time, most of the solvent is removed. Thefilament, which is at first highly fluid, is concentrated in the processand is converted into the gel state via a highly viscous state. At thestage of gel formation, the filaments may still contain some solvent.After leaving the spinning column, the filaments are collected. Thesefilaments are the actual starting material for the production of carbonand graphite fibers.

The fibrous starting material is now converted in the conventionalmanner either continuously or intermittently into fibers consistingsubstantially of more than 97 percent of carbon by increasing thetemperature to about l,000 C. 2,000 C.; heating must be carried out in astream of an inert gas at a temperature of at least about 400 C. In somecases, the starting fibers are pretreated before the actualcarbonization process. This pretreatment may consist of a special gastreatment, for example with HCl, C1 N0 or 0 either to improve thebehavior during carbonization or to render the fibers infusible.

In any particular case, the temperature treatment depends on thestarting material used for providing the carbon. The measures describedin the patent literature for the known processes for the production ofcarbon fibers may be used as a guide for successful carbonization.

Carbon fibers may also be graphitized by a thermal treatment at atemperature from about 2,000 C. to about 3,000 C. under a protectivegas.

The carbon and graphite fibers produced according to the invention maybe used for numerous purposes. Yarns, woven fabrics, felts and waddingcan be produced by conventional processes, and these products may beused, for example, for high temperature insulation, as filters for hot,corrosive gases and liquids, as reinforcing components in compositematerials and as catalysts and catalyst carriers.

The following Examples serve to illustrate the range of application ofthe process according to the invention. All concentrations are given inpercent by weight, e.g. 10 percent; which means that 10 grams of solidare dissolved in 90 grams of liquid.

Example 1 300 g of an aqueous 40 percent ammonium lignin sulfonatesolution (SAP/N of Zellstoff Waldhof) were mixed with 100 g of a 2percent aqueous polyethylene oxide solution (WSR 301 of UCC with [1;]9.15) and 45 g of water. The solution was homogenized with theintroduction of ammonia gas up to a pH of 10. The filtered spinningsolution which contained 27 percent of ammonium lignin sulfonate and0.45 percent of polyethylene oxide was spun in a column which was heatedto 80 C. and washed with dry air. The spun filaments were taken up on arotating drum. The spinning cake removed from the drum was heated from100 to 250 C. in air in the course of 1 hour. The fibers were thenheated in a stream of nitrogen, first to 400 C. at a rate of temperatureincrease of 40 per hour and finally to 1,000 C. at a rate of temperatureincrease of 150 per hour. Flexible carbon fibers were obtained (carbonyield: 36 percent). A part of the carbon fibers was subjected to agraphitization treatment by heating for 2 hours to 2,600 C. under anargon atmosphere.

Similarly prepared 40 percent and 27 percent ammonium lignin sulfonatesolutions are not spinnable to any measurable extent without theaddition of polyethylene oxide.

Example 2 300 g of dextrin, 300 g of glacial acetic acid and 300 g ofwater were boiled until completely dissolved. 430 g of the filteredsolution were concentrated by evaporation to 320 g and mixed with 214 gof a 2 percent aqueous solution of a copolymer of acrylic acid andacrylamide (Praestol 2935 of Stockhausen having an inherent viscosity of(In 1 r)/c 35.0) to form a spinning solution which contained 24 percentdextrin and 0.8 percent of acrylic acid/acrylamide copolymer. Thissolution was spun as described in Example 1. The dextrin filaments werekept under nitrogen at 220 C. for hours. The fibers were then heated ina stream of nitrogen to 400 C. at a rate of temperature increase of 10C. per hour and then to 1,000 C. at a rate of temperature increase of150 per hour. Flexible carbon fibers were obtained (carbon yield: 18percent). A 24 percent dextrin solution prepared in a similar mannerwithout the thread forming substance has a spinnability of only 3 cm.

Without the addition of polyethylene oxide, the fish I glue solution wasentirely unspinnable. Example 4 300 g of gelatine were dissolved in 300g of hot water and mixed with 300 g of glacial acetic acid and 600 g ofa 2 percent aqueous solution of an acrylic acid/acrylamide copolymer(Praestol 2935 of Stockhausen, viscosity (ln '1 .r)/c 35.0). Thesolution, which contained 0.8 percent of an acrylic acid/acrylamidecopolymer in addition to 20 percent of gelatine, was spun into gelatinefilaments as in Example 1. The gelatine fibers were converted intocarbon fibers (carbon yield: 21 percent) by carbonization in a stream ofnitrogen (5 hours kept at 220 C., heated up to 400 C. at'a rate oftemperature increase of 30 per hour, and up to 1,000 C. at a rate ofincrease of 150 per hour). A 10 percent gelatine solution prepared in asimilar manner without the fiber-forming substance is not spinnable.Example 5 v A spinning solution containing 8.8 percent of alginic acidand 0.5 percent of acrylic acid/acrylamide copolymer was obtained bydissolving g of alginic acid in 560 g of formamide and then thoroughlyhomogenizing this solution with 680 g of a 1 percent solution informamide of the acrylic acid/acrylamide copolymer used in Examples 2and 4, and the resulting product was spun as in the previous examples toproduce alginic acid filaments. Carbon fibers could be obtained fromthese filaments by carbonization in a manner analogous to Example 2.Without the fiberforming substance, an 8.8 percent alginic acid solutionin formamide was not spinnable. Example 6 33 g of starch (amyliumsolubile of Merck), 33 g of water and 33 g of glacial acetic acid wereconcentrated by boiling to 62 g. After the addition of 15.5 g of water,

82.5 g of 2 percent aqueous acid/acrylamide copolymer solution (seeExamples 2 and 4) and 5 g of 27 g of casein were dissolved in diluteaqueous ammonia and adjusted to a concentration of 20 percent. Aspinning solution containing 12.5 percent of casein and 0.75 percent ofpolyethylene oxide was obtained by the addition of 37.5 g of 2 percentaqueous polyethylene oxide, using the same polyethylene oxide as inExamples l and 3. This spinning solution was spun in a manner analogousto Example 1 to produce casein filaments. Carbon fibers (carbon yield:22 percent) were obtained from these filaments by carbonization asdescribed in Example 2. A solution prepared in a similar manner with12.5 percent of casein but without the addition of polyethylene oxide isentirely unspinnable. Example 8 Polyvinyl acetate having a degree ofpolymerization of about 430 was made up into a 30 percent solution inmethylene chloride. This solution was not spinnable. By the addition of20 g of 3 percent solution of polymethylmethacrylate (degree ofpolymerization DP 15,000) in methylenechloride to l g of the polyvinylacetate solution, a spinning solution was obtained which contained 25percent of polyvinyl acetate and 0.5 percent of polymethylmethacrylate.This spinning solution was spun as in Example 1 to produce polyvinylacetate filaments. Since polyvinyl acetate melts above approximately 100C., the spun filaments first had to be rendered infusible. For thispurpose, a part of the fibers was treated for 2 hours at roomtemperature with a stream of nitrogen of l/h which before its entry intothe reaction chamber had been charged with SO by passing it through 60percent oleum. The fibers which were colored black by the S0 treatment,were heated to 1,000 C. in a stream of nitrogen within 3 hours. Thecarbon yield was 19 percent. This is very different from the case ofpolyvinyl acetate which had been heated to 1,000 C. under nitrogenwithout previous SO treatment and in which the carbon yield was only 5.3percent. Example 9 35 g of naphthol-l-disulfonic acid-(3,8) weredissolved in 65 g of a 9 percent ammonia solution. The solution was notspinnable. A spinning solution containing 24.8 percent ofnaphthol-l-disulfonic acid- (3,8) and 0,57 percent of polyethylene oxidewas obtained by the addition of 41 g of a 2 percent aqueous polyethyleneoxide solution, using the same polyethylene oxide as in Examples 1, 3and 7. This spinning solution was spun into filaments in a manneranalogous to Example 1. Carbonization under nitrogen (rate of heating to400 C.: 57 C./h and between 400 C. and 1,000 C.: 170 C./h) yieldedflexible carbon fibers (carbon yield: 40 percent) What is claimed is:

1. In the production of carbon fibers wherein a carbon-containingfiber-forming material is extruded in solution, the solution isconverted to solid fibrous,

material, and the fibrous material is carbonized, the improvement whichcomprises forming said solution by dissolving in a solvent to aconcentration of about 0.001 to 10 percent by weight at least onefiber-forming linear high polymer having a degree of polymerization inexcess of about 2,000, and a greater amount of a carbon sourcecomprising at least one carbonizable carbon-containing organic materialhaving a softening or melting point in excess of about 80 C.'and adegree of polymerization below about 2,000, whereby said fibenforminglinear high polymer imparts to said solution a spinnability of at least50 cm.

2. Process according to claim 1, wherein the solution has a spinnabilityof at least 100 cm.

3. Process according to claim 1, wherein the solution has a spinnabilityof at least 200 cm.

4. Process according to claim 1, wherein the carbonized fiber isthereafter graphitized.

5. Process according to claim 1, wherein, said carbon source is amaterial leaving a carbon residue after carbonization which is at leastabout 10 percent by weight of the original material and, when dissolvedalone in said solvent to a concentration of 10 percent, has aspinnability of less than about 10 cm.

6. Process according to claim 5, wherein said solvent is volatile andsaid solution is converted to fibrous material by dry spinning.

7. Process according to claim 1, wherein said solution comprises anaqueous solution of said fiber-forming material and said carbon source.

8. Process according to claim 7, wherein said carbon source is at leastone of lignin, derivatives of lignin, carbohydrate derivatives andproteins.

9. Process according to claim 8, wherein the derivatives of lignin arelignin sulfonic acid and alkali metal, alkaline earth metal, andammonium salts of lignin sulfonic acid.

10. Process according to claim 1, wherein said carbon source comprises amonomer or a polymer having a degree of polymerization less than about50.

11. Process according to claim 1, wherein said carbon source is selectedfrom vinyl polymers, polyethers, polyesters, polyanhydrides,polyurethanes, polyureas, polyamides, phenol formaldehyde resins,polyolefins, and mixtures, derivatives or copolymers thereof.

12. Process according to claim 1 1, wherein after conversion of thesolution into fibrous material, the fibrous material is treated torender said carbon source infusible during subsequent carbonization.

13. Process according to claim 1, wherein said solution contains saidfiber-forming high polymer in a concentration of about 0.01 to 5 percentby weight.

14. Process according to claim 13, wherein said fiber-forming highpolymer is at least one of polystyrene, polyisobutylene,polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers,diolefin polymers, polydienes, polyethylene oxide, substitutedpolyethers and thioethers, polyesters, polyamides, polypeptides,polysaccharides, polysiloxanes, and polyacrylamide or acrylicacid/acrylamide copolymers or their alkali metal or ammonium salts.

15. Process according to claim 8, wherein said fiberforming high polymeris selected from polyethylene oxide, polyacrylamide, and acrylicacid/acrylamide copolymers or their alkali metal ammonium salts orsubstituted ammonium salts having an inherent viscosity (In 1; r)/cabove 4 (determined at a shearing stress r 0.98 dynlcm' 25 C., pH 7,0.05 percent solution with 0.1 percent NaCl).

16. Process according to claim 12, wherein said fiber-forming highpolymer is at least one of polystyrene, polyisobutylene,polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers,diolefin polymers, polydienes, polyethylene oxide, substitutedpolyethers and thioethers, polyesters, polyamides, polypeptides,polysaccharides, polysiloxanes, polyacrylamide, and acrylicacid/acrylamide copolymers or their alkali metal, ammonium, andsubstituted ammonium salts present in the solution in a

2. Process according to claim 1, wherein the solution has a spinnabilityof at least 100 cm.
 3. Process according to claim 1, wherein thesolution has a spinnability of at least 200 cm.
 4. Process according toclaim 1, wherein the carbonized fiber is thereafter graphitized. 5.Process according to claim 1, wherein, said carbon source is a materialleaving a carbon residue after carbonization which is at least about 10percent by weight of the original material and, when dissolved alone insaid solvent to a concentration of 10 percent, has a spinnability ofless than about 10 cm.
 6. Process according to claim 5, wherein saidsolvent is volatile and said solution is converted to fibrous materialby dry spinning.
 7. Process according to claim 1, wherein said solutioncomprises an aqueous solution of said fiber-forming material and saidcarbon source.
 8. Process according to claim 7, wherein said carbonsource is at least one of lignin, derivatives of lignin, carbohydratederivatives and proteins.
 9. Process according to claim 8, wherein thederivatives of lignin are lignin sulfonic acid and alkali metal,alkaline earth metal, and ammonium salts of lignin sulfonic acid. 10.Process according to claim 1, wherein said carbon source comprises amonomer or a polymer having a degree of polymerization less than about50.
 11. Process according to claim 1, wherein said carbon source isselected from vinyl polymers, polyethers, polyesters, polyanhydrides,polyurethanes, polyureas, polyamides, phenol formaldehyde resins,polyolefins, and mixtures, derivatives or copolymers thereof. 12.Process according to claim 11, wherein after conversion of the solutioninto fibrous material, the fibrous material is treated to render saidcarbon source infusible during subsequent carbonization.
 13. Processaccording to claim 1, wherein said solution contains said fiber-forminghigh polymer in a concentration of about 0.01 to 5 percent by weight.14. Process according to claim 13, wherein said fiber-forming highpolymer is at least one of polystyrene, polyisobutylene,polymethylmethacrylate, polyisoprene, vinyl polymers and copolymers,diolefin polymers, polydienes, polyethylene oxide, substitutedpolyethers and thioethers, polyesters, polyamides, polypeptides,polysaccharides, polysiloxanes, and polyacrylamide or acrylicacid/acrylamide copolymers or their alkali metal or ammonium salts. 15.Process according to claim 8, wherein said fiber-forming high polymer isselected from polyethylene oxide, polyacrylamide, and acrylicacid/acrylamide copolymers or their alkali metal ammonium salts orsubstituted ammonium salts having an inherent viscosity (ln eta r)/cabove 4 (determined at a shearing stress Tau 0.98 dyn/cm2, 25* C., pH 7,0.05 percent solution with 0.1 percent NaCl).
 16. Process according toclaim 12, wherein said fiber-forming high polymer is at least one ofpolystyrene, polyisobutylene, polymethylmethacrylate, polyisoprene,vinyl polymers and copolymers, diolefin polymers, polydienes,polyethylene oxide, substituted polyethers and thioethers, polyesters,polyamides, polypeptides, polysaccharides, polysiloxanes,polyacrylamide, and acrylic acid/acrylamide copolymers or their alkalimetal, ammonium, and substituted ammonium salts present in the solutionin a concentration of about 0.01 to 5 percent and the solution is formedinto fibrous material by dry spinning.